The present invention relates to a yarn tensioning device and more particularly to a yarn tensioning device of the type having a housing with a yarn inlet and a yarn outlet for travel of yarn through the housing wherein the housing has an annular seat formed in the yarn inlet and a yarn tensioning element in engagable on the seat for applying tension to a yarn traveling between the seat and the tensioning element.
Yarn tensioning devices of this type, such as disclosed and claimed in my prior U.S. Pat. Nos. Re. 30,920, 31,024 and 31,041 have proven to be highly successful in providing reliable uniform tensioning of yarn in various types of yarn and thread processing equipment, such as in textile winders, warpers, weaving looms, knitting machines and the like and in other types of equipment in textile and other fields that involve processing or handling of traveling strand material. Previous devices of this general type have been provided with removable caps or retaining elements that allow removal and replacement of the tensioning elements, which has been considered advantageous in allowing the change of elements for operation with yarns of different size or running charactristics. However, this has led to improper substitution and addition of elements with resulting non-uniform and/or imperfect tensioning. According to one feature of the present invention this problem is overcome by using a cap that is fixed against removal and has a yarn passageway therein smaller than the size of the tensioning element so that once the device is assembled with the tensioning element in the housing and the cap fixed thereon the tensioning element cannot be replaced and additional tensioning elements cannot be inserted. In this regard, it has been determined that a selected size of tensioning element is normally suitable for use with a wide range of yarn types and characteristics and with a wide range of types of equipment, such that changing of tensioning elements or removing or adding elements is not necessary and when such changes are made it can result in problems when not done with expertise in selection of the elements to be used.
When using a cap on the housing of a tensioning device of this type, it is sometimes difficult to initially thread the yarn through the housing and cap as a threading rod may be obstructed by the inner surface of the cap and threading by air can also be disrupted by the shape of the inner surface of the cap. This is particularly a problem where the cap is formed with a small passageway for the purpose mentioned above of preventing removal or insertion of tensioning elements. To alleviate this problem, the present invention forms the cap with a frusto-conical inner annular surface tapering from the housing to the passageway so that a threading rod will be guided along this surface into the passageway and an air threading blast will also be directed toward the passageway.
The aforementioned frusto-conical inner annular surface of the cap further can provide enhanced yarn behavior in certain yarns as the yarns pass through the device and contact this inner annular surface. Enhanced behavior of some yarns is also obtained by another feature of the present invention wherein the outer annular surface of the cap is formed with two sequentially adjacent frusto-conical surface portions of progressively greater taper forming a yarn contacting annular juncture therebetween. Thus, as the yarn passes over this surface and contacts this juncture improved behavior of the yarn is obtained, particularly with high torque yarn where this action results in a relaxation of the yarn.
Improved handling of yarn is further facilitated by another feature of the present invention wherein the cap is formed with a relieved peripheral outer annular surface that eliminates yarn contact with an otherwise sharp outer edge of the cap.
In the prior tensioning devices of this general type, the tensioning elements are commonly in the form of spherical elements or balls that are free to rotate under the influence of the yarn as the yarn travels through the device, thereby reducing friction and providing a smooth tensioning application. However, in some applications a free rolling ball is a disadvantage, particularly when the yarn stops traveling and the ball rolls down onto the seat against the yarn, with the rolling of the ball disrupting yarn so as to create picks and at times causing the yarn to wind on the ball. This is particularly noticeable with quick stopping of high speed operations, such as in shuttleless loom weaving and high speed warping. To overcome this problem, a further feature of the present invention provides for a tensioning element that is sufficiently non-spherical to preclude substantial rotation of the element during travel of the yarn therepast.